The present invention is a device for the automatic control of the feed of a tubular wire, in particular made of precious material used in the goldsmith industry. It is known to use tubular wire in the goldsmith industry, made of precious or non-precious material, for the production of chains, bracelets and similar products of jewelry or trinkets shops. The use of tubular wire, is particularly convenient, in that it allows a remarkable reduction of the weight, and consequently of the cost, of the finished product without modifying appreciably the aesthetic appeal.
This kind of wire, known also as hollow wire, is generally obtained from a ribbon of the desired material, for instance gold, and from another wire of another non-precious material, for instance copper, aluminum or iron, that acts as a support or core upon which said ribbon is folded over, for instance by a process of drawing. The composite wire thus obtained is suitable for being worked on the machine tools commonly used in the goldsmith industry without danger of damage or deformation. When the desired product has been obtained, the core of non-precious material is eliminated by means of suitable solvents that are inert in respect of the external precious coating. This kind of wire shows a longitudinal cut or groove delimited by the opposite edges of the starting ribbon applied over the internal core. This groove does not develop parallel to the axis of the wire, but it has a generally helicoidal trend due both to the operative modes with which the application of said ribbon is made, and to the manner in which the wire is wound on the take-up coils provided for this purpose. It is clear that in the finished products the groove in question should not be easily visible, i.e. it should be in the internal part of the surface of the several links. The basic problem encountered therefore in the use of this kind of wire is that it should be fed to the machine tool in such a way so that the groove in question is placed always in the same predetermined position.
Presently the control of the position of the groove is made upon sight by the operator of the machine, who provides manually, during the unwinding of the wire from the coil, an angular displacement with respect to the unwinding axis of the coil itself in one direction or another to compensate for the displacement of the groove and to bring it back to the predetermined position. It is clear that in this way the quality of the obtained product will depend in a large measure upon the skill and the carefulness of the operator, as well as upon the dimensions of the wire in movement, because it is more difficult to follow the groove by sight with the decrease of the diameter of the wire. Moreover, each completely automatic machine tools needs an operator performing solely the control of the feed.